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Sinabung - An erupting volcano 630km from Singapore

22 Nov 2013

Executive Summary

Sinabung is a stratovolcano, a volcano built up by many layers of lava and ash, located in the northern part of the island of Sumatra, Indonesia. Sinabung used to be dormant until its eruption in 2010. After three quiet years, renewed activity occurred in September 2013 - go to the Center of Volcanology and Geological Hazard Mitigation (CVGHM) website for accurate information on the current volcanic activity. 

It is a difficult task to predict the behaviour of a volcano like Sinabung that has been dormant for a long period. Decisions regarding alert levels and evacuation orders rely on numerous parameters currently monitored by the CVGHM. The Earth Observatory of Singapore conducts fundamental research on long-term behaviour of volcanic systems in Southeast Asia in close partnership with local institutes and authorities.

 

Overview

Sinabung is one volcano among many others in Southeast Asia. A long arc of active volcanoes forms the backbone of the Indonesian Archipelago, from Sumatra and Java to Papua-New Guinea, stretching over more than 4000 km. About fifty of them have erupted during the last century. Such a concentration of very active volcanoes is not due to chance: the region’s tectonic settings account for it.

These numerous volcanoes sit on top of subduction zones, where one plate moves toward and slides under another. This process causes material in the Earth's mantle and crust to melt; this molten magma, hotter and less dense than the surrounding rock, rises up towards the surface, where it creates volcanism.

 

Predicting Volcanic Behaviour

Anticipating the future relies on understanding the past, and thus expanding the studies of past volcanic activity is necessary. Histories of past eruptions for a number of volcanoes remain poorly known, in particular those that are dormant. Geological studies of volcanic deposits provide a window into the history and behaviour of past eruptions: their frequency, size, and variability in explosivity. This information is particularly valuable given that violent eruptions are infrequent. Therefore, a volcano that has not erupted in our lifetimes, or in the past few generations, may still pose a great threat. 

The threat from Sumatran volcanoes is difficult to estimate, as knowledge on past volcanic activity is sparse. The most active volcanoes in Sumatra have only exhibited small eruptions in historic times. However, the size, shape and crater dimensions of some Sumatran volcanoes show evidence of large eruptive events in the past.

Sinabung’s past eruptive history in particular is not well known. The Global Volcanism Program refers to an “uncertain” eruption back in 1881, although a report by scientists from the CVGHM mentions a period of dormancy longer than 400 years. In 1912 solfataras (fumaroles that emit sulphurous gases) were reported.

In any event, CVGHM reports in 2010 show that the volcano erupted from the end of August to the end of September. During this period several explosions produced ash plumes that rose up to 5km above the crater. After three years of quiescence, the unrest started again in September 2013, with several eruptions that produced ash plumes as high as 8km above sea level.

The study of Sinabung's eruptive history and the main characteristics of its eruptive products will help determine the likelihood of a large-scale eruption of this volcano.

The Earth Observatory of Singapore does not currently study or monitor this particular volcano.  

 

Plugged vs. Unplugged Volcanoes

Volcanoes display a wide variety of eruptive styles that are linked in large part to how gas is released.  If a volcano allows gases contained in the magma to flow freely out of the system, then eruptions will mostly be non-explosive. On the contrary, if the gases accumulate in a volcano, pressure in the system increases (like in a pressure-cooker) and eruptions will tend to be more explosive.

That is why volcanoes can be roughly subdivided in two categories: plugged volcanoes – that exhibit minor degassing or no degassing at all – versus unplugged volcanoes – that are openly degassing. However, it is important to keep in mind that changes in eruption style and behaviour may occur at a given volcano.

Unplugged volcanoes produce mostly small and frequent eruptions, although some of them can be violent and deadly. In general, people living in the vicinity of this type of volcano are well aware of the risk. Scientists are generally able to forecast upcoming eruptions thanks to the long eruptive history and repetitive characteristics of these volcanoes. However, due to their unplugged nature, precursory signals (e.g. seismicity, deformation of the volcano) are often hard to catch because internal pressure does not increase much. Mayon, for example, has erupted recently in August-September 2006, in December 2009, and in May 2013. Despite all the instruments deployed on the cone of this stratovolcano, the last eruption could not be forecasted, which is a reminder that science is never infallible.

Plugged volcanoes, on the contrary, can be dormant for centuries before they awaken and erupt, sometimes quite violently. The behaviour of this type of volcano is very hard to predict. Although the precursory signals of awakening are easier to detect than for unplugged volcanoes, it is impossible to equip all dormant volcanoes with a dense array of monitoring instruments. Scientists therefore need to study past magmatic and eruptive processes and constantly upgrade geophysical, geochemical, and hydrologic monitoring to anticipate the next eruption. Pinatubo, the volcano that erupted in 1991 in the Philippines is a perfect example of this volcanologists’ nightmare: after five centuries of dormancy, this volcano that everybody thought inactive produced one of the largest eruption of the century.

Sinabung awakened from centuries of dormancy in August 2010. Since a plugged volcano’s range of behaviour is extremely wide, and since Sinabung’s history is mostly unknown, it is difficult to assess its current potential for future eruptions. One very important way that scientists can better forecast chances of future eruptions is to deploy field instruments and closely monitor the volcano’s activity. CVGHM is currently doing this at Sinabung.

 

The Centre of Volcanology and Geological Hazard Mitigation (CVGHM), Indonesia

The CVGHM (know in Indonesia as PVMBG, Pusat Vulkanologi dan Mitigasi Bencana Geologi) is the institute responsible for volcanic and seismic risks mitigation in Indonesia.

The CVGHM prepares policies, norms and procedures related to geological hazards in the country. It conducts independent research on volcanoes in Indonesia, and provides advice to the communities regarding engineering and urban planning in the vicinity of active volcanoes.

Researchers of the CVGHM monitor volcanoes in Indonesia, and are responsible for issuing evacuation orders in a timely fashion to the threatened populations.

To learn about the different levels of alert during the 2010 eruption, and the alert level for the ongoing eruption, connect to CVGHM website page about the Sinabung, here and here.

 

The Volcano Group at the Earth Observatory of Singapore

The Volcano Group at EOS conducts geologic, geochemical and geophysical studies to improve our understanding of volcanic activity, and more particularly the processes related to eruptions. EOS research in this field is designed to produce knowledge and tools that will aid forecasting of volcanic eruptions, assessment of their environmental and societal impacts, and efforts to mitigate the hazards.

EOS main efforts in volcanology focus on three different approaches:

  • Fundamental research on all processes from the genesis of the magma to the eruption itself.
  • In collaboration with PHIVOLCS and CVGHM, EOS has considerably increased the monitoring instrumentation on three selected volcanoes in Southeast Asia: Mayon in Southeast Luzon, Philippines; and Gede and Salak in West Java, Indonesia. These volcanoes span a wide range of degassing behaviours: Mayon is unplugged, while Gede and Salak are plugged. The nuances displayed by these volcanoes make them very valuable for fundamental research, and enable scientists to better understand the behaviours of other volcanoes in the region.
  • Hosting, and managing WOVOdat, a global volcanic unrest database that will enable better forecasts through comparative studies of active volcanoes.

The Knowledge Capsule below summarizes the work of Assistant Professor Fidel Costa, one of the researchers of EOS Volcano Group: